In 5th Generation mobile networks or wireless systems (5G) or 5G New Radio (NR), spatial quasi co-location (QCL) has been introduced as a new concept. Two transmitted reference signals from a transmitter (e.g., base station) are said to be spatially QCL at a receiver (e.g., UE or terminal) if the receiving spatial characteristics of the two received reference signals are the same or similar. Spatial characteristics may be one or more of the primary angle of arrival, the receiving angular spread of the signal, the spatial correlation, or any other parameter or definition that captures spatial characteristics. The two reference signals are sometimes denoted equivalently as being transmitted/received from/by two different antenna ports. If two transmitting antenna ports of a gNB (e.g., base station) are spatially QCL at the UE, the UE may use the same receiving (RX) beamforming weights to receive both the first and second reference signals.
The use of spatial QCL is of particular importance when the UE uses analog beamforming, since the UE has to know where to direct the analog beam before receiving the signal. Hence, for 5G NR, it is possible to signal from gNB to UE that a certain previously transmitted channel state information reference signal (CSI-RS) resource or CSI-RS antenna port is spatially QCL with a physical downlink shared channel (PDSCH) transmission and the PDSCH's demodulation reference signal (DMRS) transmission. With this information, the UE may use the same analog beam for the PDSCH reception as it used in the reception of the previous CSI-RS resource or antenna port.
The spatial QCL framework may also be extended to hold for transmissions from the UE. In this case, the transmitted signal from the UE is spatially QCL with a previous reception of a signal received by the UE. If the UE makes this assumption for the transmission, it means that the UE is transmitting back a signal in an analog transmit (TX) beam which is the same or similar to the RX beam previously used to receive a signal. Hence, the first Reference Signal (RS) transmitted from the gNB is spatially QCL at the UE with a second RS transmitted from the UE back to the gNB. This is useful in case the gNB uses analog beamforming since the gNB then knows from which direction to expect a transmission from the UE and may therefore adjust its beam direction just before the actual reception.
In 5G NR, a primary synchronization signal (PSS), a secondary synchronization signal (SSS), a physical broadcast channel (PBCH), and possibly a tertiary synchronization signal (TSS) will be used in a synchronization signal (SS) block. The SS block will likely span four orthogonal frequency division multiplex (OFDM) symbols. Multiples of such SS blocks may be transmitted on different beams in different beamforming directions, and thus each SS block may benefit from the antenna gain of the corresponding beam. The drawback is that multiple SS blocks require multiples of four OFDM symbols to be used to cover the whole gNB area with such beams. Further, the narrower the beam, the better the coverage per beam but the larger the overhead from transmitting SS blocks. Hence, there is a tradeoff between coverage and overhead. Also, SS block beams are wider than data beams, which may be very narrow to provide very high antenna gain in order to maximize the signal to interference plus noise ratio (SINR) at the receiver.
Furthermore, existing air interface solutions do not provide robust communications between a UE and a gNB when utilizing narrow beamforming such as in the millimeter wave frequencies. This is even more apparent with analog beamforming that requires knowing where to direct a beam. Since beams are very narrow (e.g., down to a few degrees in beam width) failure to direct this narrow beam in the right direction may lead to loss in connection and interruption in data throughput. Also, the UE may need to direct the beam in a robust manner when receiving synchronization signals and broadcast signals (e.g., common search space physical downlink control channel (PDCCH)) or transmitting physical random access channel (PRACH) or beam recovery signals while at the same time receiving and transmitting dedicated signals that require high gain or narrow beams (e.g., PDSCH, physical uplink shared channel (PUSCH), and UE-specific search space PDCCH). In addition, the UE may need to set the UE beam direction without dedicated beam indication signaling from gNB to UE. In an NR system, there is also a need to transmit both narrow and wide width beams, where narrow beams may be used for the transmission of unicast messages while wide beams may be used for the transmission of multicast or broadcast messages.
Accordingly, there is a need for improved techniques for determining transmitter and receiver configurations for a wireless device. In addition, other desirable features and characteristics of the present disclosure will become apparent from the subsequent detailed description and embodiments, taken in conjunction with the accompanying figures and the foregoing technical field and background.
The Background section of this document is provided to place embodiments of the present disclosure in technological and operational context, to assist those of skill in the art in understanding their scope and utility. Unless explicitly identified as such, no statement herein is admitted to be prior art merely by its inclusion in the Background section.